Heat exchanger

ABSTRACT

In a heat exchanger, a tube is adapted to exchange heat between a first fluid flowing therein and a second fluid flowing through outside of the tube, and an inner fin is disposed in the tube to divide a flow passage in the tube into a plurality of flow paths. The inner fin includes a plurality of fin portions with different specifications, and the fin portions are arranged in series with respect to a flow direction of the first fluid. Furthermore, the fin portion with the smallest flowing resistance of the first fluid among the plurality of fin portions is arranged on an upstream side of the flow direction of the first fluid with respect to at least an another fin portion. Accordingly, heat exchange performance in the entire heat exchanger can be effectively improved.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2007-303289 filed on Nov. 22, 2007, the contents of which are incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger. The heat exchanger can be suitably used as an intercooler for cooling intake air to be supplied to an internal combustion engine, for example.

BACKGROUND OF THE INVENTION

Conventionally, a heat exchanger such as an intercooler performs heat exchange between cooling air and intake air to be drawn into an internal combustion engine so as to cool the intake air (for example, JP-A-2006-90305). The intercooler includes inner fins inserted into tubes in which the intake air flows, thereby promoting heat exchange between the intake air and the cooling air. The inner fins have generally the same shape, that is, the same specification from an intake air inlet side of the tubes to an intake air outlet side thereof in the intercooler.

FIG. 8 shows a relationship between an intake air temperature Tg in the tube and a distance H from an intake air inlet of the tube in the intercooler, according to experiments by the inventors of the present application. As shown in FIG. 8, high-temperature intake air flowing from the intake air inlet of the tube into the tube is drastically cooled in the tube, resulting in a large difference in temperature of the intake air between the intake air inlet side and the intake air outlet side of the tube. That is, the temperature Tg of the intake air is rapidly reduced from the intake air inlet of the tube as the distance H from the intake air inlet of the tube increases. FIG. 9 shows a relationship between a flow velocity Vg of intake air and the distance H from the intake air inlet of the tube in the intercooler, according to experiments by the inventors of the present application. As shown in FIG. 9, the flow velocity Vg of intake air flowing from the intake air inlet of the tube into the tube has a large difference between the intake air inlet side and the intake air outlet side of the tube. That is, the flow velocity Vg of the intake air is rapidly reduced from the intake air inlet of the tube as the distance H from the intake air inlet of the tube increases. At this time, the use of the inner fins with the same specification from the intake air inlet side to the outlet side as described above may drastically increase the loss in pressure at the intake air inlet side, resulting in reduction in heat exchange performance of the whole intercooler.

Furthermore, as shown in FIG. 8, the temperature Tg of intake air becomes very low on the intake air outlet side of the tube, as compared to the intake air inlet side of the tube. Thus, the difference in temperature between the intake air and the cooling air becomes small on the intake-air outlet side, and thereby it may be difficult to exchange heat between the intake air and the cooling air. At this time, the use of the inner fins having the same specification from the intake air inlet side to the intake air outlet side described above may be difficult to effectively perform heat exchange at the intake air outlet side of the tube.

SUMMARY OF THE INVENTION

In view of the foregoing problems, it is an object of the present invention to provide a heat exchanger which can effectively improve heat exchange performance.

It is another object of the present invention to provide a heat exchanger having a tube in which a plurality of fin portions with different specifications are located in the tube.

According an aspect of the present invention, a heat exchanger includes a tube having therein a flow passage through which a first fluid flows, and an inner fin provided in the tube. The tube is adapted to exchange heat between the first fluid and a second fluid flowing through an outer periphery of the tube, and the inner fin is located in the tube to promote the heat exchange between the first fluid and the second fluid. The inner fin is configured to divide the flow passage in the tube into a plurality of flow paths. Furthermore, the inner fin includes a plurality of fin portions with different specifications, and the fin portions are arranged in series with respect to a flow direction of the first fluid. In addition, the fin portion with the smallest flowing resistance of the first fluid among the plurality of fin portions is arranged on an upstream side of the flow direction of the first fluid with respect to at least an another fin portion. Accordingly, the heat exchange performance in the heat exchanger can be effectively increased.

The phrase “the fin portion with the smallest flowing resistance of the first fluid is arranged on the upstream side of the flow direction of the first flow with respect to at least an another fin portion” as used herein means not only that the fin portion with the smallest flowing resistance of the first fluid is arranged only on the upstream side of the first fluid flow with respect to the other fin portions, but also the following case. That is, the phrase also means that the fin portion with the smallest flowing resistance of the first fluid is arranged on the upstream side of the first fluid flow, and the fin portion with the smallest flowing resistance of the first fluid may be also arranged on the downstream side of the first fluid flow with respect to the other fin portion. When the fin portion with the smallest flowing resistance of the first fluid is arranged on the upstream side of the flow direction of the first fluid with respect to at least an another fin portion with a flowing resistance of the first fluid larger than the smallest flowing resistance, the shape or the like of the other fin portion(s) can be suitably changed.

For example, the fin portion with the largest flowing resistance of the first fluid among the plurality of fin portions may be arranged on a downstream side of the flow direction of the first fluid with respect to the other fin portion.

Alternatively, the fin portions may be arranged symmetrically with respect to a center line of the inner fin in the flow direction of the first fluid. Furthermore, the fin portions may be constructed of at least first and second different kinds of fin portions. For example, the plurality of fin portions may include a straight fin portion and a louver fin portion, and the straight fin portion may be arranged on an upstream side of the flow direction of the first fluid with respect to the louver fin portion.

In this case, the straight fin portion may have a plurality of wall surfaces extending linearly in the flow direction of the first fluid, and the wall surfaces may be configured to divide the flow passage of the tube into the plurality of flow paths. Furthermore, the louver fin portion may include a plurality of flat portions substantially in parallel to the flow direction of the first fluid, and a plurality of louvers may be provided at the flat portions along the flow direction of the first fluid. As an example, the louvers may be formed by cutting and raising a part of the flat portion.

Alternatively, the plurality of fin portions may include a straight fin portion and an offset fin portion, and the straight fin portion may be arranged on an upstream side of the flow direction of the first fluid with respect to the offset fin portion. In this case, straight fin portion has a plurality of wall surfaces extending linearly in the flow direction of the first fluid, and the wall surfaces are configured to divide the flow passage of the tube into the plurality of flow paths. Furthermore, the offset fin portion including wall portions are arranged in a zigzag shape along the flow direction of the first fluid, and the wall portions are configured to divide the flow passage of the tube into the plurality of flow paths.

Alternatively, the inner fin may be a louver fin that includes a plurality of flat portions substantially in parallel to the flow direction of the first fluid, and a plurality of louvers provided at the flat portions along the flow direction of the first fluid. In this case, the fin portions are configured to have different louver pitches in the louvers, and the fin portion with the largest louver pitch among the plurality of fin portions is arranged on an upstream side of the flow direction of the first fluid with respect to at least an another fin portion.

Alternatively, in the heat exchanger, the fin portions may have different fin pitches. In this case, the fin portion with the largest fin pitch among the fin portions is arranged on an upstream side of the flow direction of the first fluid, with respect to at least an another fin portion.

In any above-described structure of the heat exchanger, the fin portions may be continuously arranged in the flow direction of the first fluid such that flow resistances of the first fluid in the fin portions are increased as toward downstream in the flow direction of the first fluid. Furthermore, in the heat exchanger, the first fluid flowing in the tube generally may have a temperature higher than that of the second fluid.

Furthermore, the heat exchanger may include a plurality of the tubes stacked in a stacking direction, and a plurality of outer fins each of which is located between adjacent tubes. As an example, the first fluid is an intake air to be supplied to an internal combustion engine, and the second fluid is a cooling air.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments when taken together with the accompanying drawings. In which:

FIG. 1 is a front view of an intercooler according to a first embodiment of the present invention;

FIG. 2 is a cross sectional view taken along the line I-I in FIG. 1;

FIG. 3 is a cross sectional view taken along the line II-II in FIG. 2;

FIG. 4 is an enlarged perspective view showing an inner fin in the first embodiment;

FIG. 5 is a sectional view showing an inner fin when being viewed in a stacking direction of tubes according to a second embodiment of the present invention;

FIG. 6 is an enlarged perspective view showing a third fin portion of the inner fin in the second embodiment;

FIG. 7 is a sectional view showing an inner fin when being viewed in a stacking direction of tubes according to a third embodiment of the present invention;

FIG. 8 is a graph showing a relationship between an intake air temperature Tg in a tube and a distance H from an intake air inlet of the tube in an intercooler; and

FIG. 9 is a graph showing a relationship between a flow velocity Vg of intake air in a tube and a distance H from an intake air inlet of the tube in an intercooler.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A first embodiment of the present invention will be described below with reference to FIGS. 1 to 4. A heat exchanger according to the first embodiment of the present invention is typically used for an intercooler. The intercooler is configured to perform heat exchange between outside air (cooling air) and intake air for combustion to be supplied into an internal combustion engine, thereby to cool the intake air. The intake air is an example of a first fluid of the present invention, and the cooling air is an example of a second fluid of the present invention.

As shown in FIGS. 1 and 2, a core portion 1 of the intercooler includes a plurality of stacked flat tubes 2 each having a flow passage formed therein for allowing intake air to flow therethrough, inner fins 3 disposed within the flat tubes 2, and outer fins 4 each of which is disposed between the stacked flat tubes 2. The flat tubes 2 are stacked in a tube stacking direction that is perpendicular to the tube longitudinal direction and a flow direction of the cooling air, as shown in FIGS. 1 and 2. In the present embodiment, the tube 2 is made of copper or stainless material, and both the inner fin 3 and the outer fin 4 are made of copper, for example.

The outer fin 4 is formed in a wave-like shape (corrugated shape) to be bonded to the outer wall surface of the tube 2, and adapted to promote heat exchange between cooling air flowing through between the tubes 2 and intake air flowing in the tubes 2. The outer fin 4 is provided with louvers 4 a formed by cutting and raising a part of the fin to have a louver window shape in order to prevent disturbance of air flow and growing of a temperature interface layer.

The inner fin 3 is formed into a wave-like shape (corrugated shape) to be bonded to the inner wall surface of the tube 2, and adapted to promote heat exchange between the cooling air and intake air. As shown in FIG. 4, the inner fin 3 includes a plurality of wall surfaces 3 a each of which extends to connect opposite wall surfaces of the tubes 2. A flow passage in the tube 2 is divided into a plurality of thin wall flow paths 20 by the wall surfaces 3 a of the inner fin 3, as shown in FIGS. 2 and 4. The detailed structure of the inner fin 3 will be described later.

Header tanks 5 and 6 are provided on both end sides of the tubes 2 in the tube longitudinal direction, to extend in the stacking direction of the tubes 2. Each of the header tanks 5 and 6 is located to communicate with the respective tubes 2. One header tank 5 has an inlet 50 connected to a supercharger, from which intake air pressure-fed is introduced. The intake air flowing into the header tank 5 from the inlet 50 is distributed among and flows into the respective tubes 2. The other header tank 6 has an outlet 60 connected to an intake port of the internal combustion engine. The other header tank 6 is adapted to collect and recover intake air flowing from the tubes 2, so as to feed the air to an intake port of the internal combustion engine. Both header tanks 5 and 6 can be made of a metal such as copper.

FIG. 2 is a cross sectional view taken along the line I-I in FIG. 1, FIG. 3 is a cross sectional view taken along the line II-II in FIG. 2, and FIG. 4 is an enlarged perspective view showing the inner fin 3 in the first embodiment.

The inner fin 3 of the present embodiment shown in FIGS. 3 and 4 is formed by applying a roller forming method to a thin metallic material. The inner fin 3 includes the wall surfaces 3 a extending substantially in parallel to the flow direction of the intake air in the tube 2, and top parts 3 b connecting the adjacent wall surfaces 3 a. The inner fin 3 is formed in a corrugated shape when being viewed from the flow direction of the intake air. A plurality of the wall surfaces 3 a are arranged in the flow direction of cooling air (e.g., in the width direction of the tube 2), as shown in FIG. 2. The wall surface 3 a may be a flat surface as shown in FIG. 4.

The inner fin 3 of the present embodiment includes two different kinds of fin portions 31 and 32. These two fin portions 31 and 32 are arranged continuously in series in the flow direction of the intake air. One of the two fin portions 31 and 32 which is arranged on the upstream side in the intake-air flow direction is hereinafter referred to as the first fin portion 31, whereas the other arranged on the downstream side in the intake-air flow direction is hereinafter referred to as the second fin portion 32. In the present embodiment, the first fin portion 31 and the second fin portion 32 are continuously formed to be integrated as one inner fin.

The second fin portion 32 is a louver fin having a plurality of louvers 321. Specifically, the wall surface 3 a of the second fin portion 32 is integrally formed with the louvers 321 each of which has a louver window shape by cutting and raising a part of the wall surface 3 a. Each louver 321 is formed by being bent and twisted at a predetermined twist angle with respect to the wall surface 3 a as being viewed in the stacking direction of the tubes 2. A plurality of louvers 321 are provided in the wall surface 3 a along the flow direction of the intake air. A louver-to-louver passage 322 is formed between the adjacent louvers 321.

The second fin portion 32 of the present embodiment includes turning portions 323 each reversing the twisting direction of the louver 321, as shown in FIG. 3. Each turning portion 323 is positioned at a center portion of the second louver portion 32 in the flow direction of the intake air.

The first fin portion 31 does not have any louver 321, and is a straight fin including a wall surface 30 linearly extending in the flow direction of the intake air. Thus, a flowing resistance of intake air in the first fin portion 31 (hereinafter referred to as an “air flowing resistance”) is smaller than that in the second fin portion 32 with the louvers 321.

The intake air inlet side, that is, the most upstream side of the intake air flow in the tube 2 has an intake air temperature higher than that of other parts thereof, thereby making a flow velocity of intake air on the inlet side higher than that of the other parts. For this reason, providing the inner fin 3 in the tube 2 may lead to the largest loss of pressure on the intake air inlet side. Thus, in the present embodiment, the first fin portion 31 which is the straight fin having the small air flowing resistance is disposed on the intake air inlet side in the tube 2, and thereby it can reduce the loss in pressure on the intake air inlet side of the tube 2.

At this time, since the first fin portion 31 having the small air flowing resistance has relatively low heat exchange performance, the heat exchange performance on the intake air inlet side of the tube 2 may be relatively reduced in the intercooler 1. The intake air inlet side of the tube 2, however, can sufficiently have a difference in temperature between the intake air and cooling air, and thereby it can suppress the reduction in heat exchange performance on the intake air inlet side of the tube 2 to a very small level. That is, the reduction in heat exchange performance of the intake air inlet side of the tube 2 due to reduction in heat exchange performance of the first fin portion 31 is very small, as compared to the increase of the heat exchange performance of the entire intercooler due to reduction in loss of pressure on the intake air inlet side of the tube 2.

Thus, in the present embodiment, the shape of the first fin portion 31 is not limited to the straight line shape shown in FIG. 1, but may be suitably changed. For example, a first fin portion 31 having an air flowing resistance smaller than that of the second fin portion 32 can be arranged on the intake air inlet side within the tube 2. Even in this case, the heat exchange performance of the entire heat exchanger can be effectively improved.

The intake air outlet side, that is, the most downstream side of the intake air flow, in the tube 2 has an intake air temperature lower than that of the other parts thereof, resulting in a small difference in temperature between the intake air and the cooling air, making it difficult to perform heat exchange. Thus, the second fin portion 32 which is a louver fin having a large air flowing resistance (or having high heat exchange performance) is disposed on the intake air outlet side of the tube 2, and thereby it can improve the heat exchange performance on the intake air outlet side of the tube 2.

At this time, the air flowing resistance is increased on the intake air outlet side of the tube 2. The intake air temperature on the intake air output side of the tube 2 is low and thus the flow velocity of the intake air is low, so that it can suppress the amount of increase in loss of pressure on the intake air output side of the tube 2 to a very small level. That is, the reduction in heat exchange performance of the entire intercooler due to an increase in loss of pressure on the intake air outlet side of the tube 2 is very small, as compared to improvement of the heat exchange performance by disposing the second fin portion 32 having the large air flowing resistance on the intake air output side of the tube 2.

Thus, according to the present embodiment, because the second fin portion 32 having the air flowing resistance larger than that of the first fin portion 31 is disposed on the intake air outlet side of the tube 2, it can further effectively improve the heat exchange performance in the entire heat exchanger. That is, the second fin portion 32 is configured to have the higher heat exchange performance between the intake air and the cooling air in the intercooler 1, than that of the first fin portion 31, the shapes of the first fin portion 31 and the second fin portion 32 can be suitably changed.

Second Embodiment

A second embodiment of the present invention will be described below based on FIGS. 5 and 6. The same components as those in the first embodiment are designated by the same reference numerals, and a description thereof will be omitted below. FIG. 5 is a sectional view of the inner fin 3 of the second embodiment when being viewed in the stacking direction of the tubes 2. FIG. 5 of the second embodiment is a drawing corresponding to FIG. 3.

As shown in FIG. 5, an inter fin 3 of the present embodiment includes three different kinds of fin portions 31 to 33. The three fin portions 31 to 33, namely, the first fin portion 31, the third fin portion 33, and the second fin portion 32 are arranged continuously in that order from the upstream side of the intake air flow. The first fin portion 31 is a straight fin similar to that in the first embodiment. The second fin portion 32 is a louver fin similar to that in the first embodiment.

FIG. 6 is an enlarged perspective view showing the third fin portion 33 in the second embodiment. As shown in FIG. 6, the third fin portion 33 of the present embodiment has a corrugated sectional shape in cross section substantially perpendicular to the flow direction of the intake air, or when being viewed in the flow direction of the intake air. The sectional shape is formed by alternately positioning and bending convex portions 331 on one side and on the other side. The third fin portion 33 includes cut-up portions 332 formed by partially cutting and raising the fin 33 in the flow direction of the intake air. The third fin portion 33 is an offset fin in which wave-shaped portions formed by the cut-up portions 332 are offset by adjacent wave-shaped portions in the intake-air flowing direction when being viewed in the intake-air flowing direction. The convex portions 331 of the third fin portion 33 are located in contact with the inner wall surface of the tube 2.

The inside of the tube 2 is divided into a plurality of flow paths by the third fin portion 33. The flow paths divided in the tube 2 are partially offset in the intake-air flowing direction. That is, wall portions 333 for dividing the inside of the tube 2 into the flow paths are arranged in a zigzag shape along the intake-air flowing direction. Upon viewing the third fin portion 33 in the intake-air flowing direction, the concave portions 331 are adjacent to each other on the same side, that is, on one side and on the other side, in the intake-air flowing direction. The concave portions 31 are positioned so as to be offset from each other.

Returning now to FIG. 5, the first fin portion 31 serving as the straight fin has the smaller air flowing resistance than that of each of the second fin portion 32 serving as the louver fin and the third fin portion 33 serving as the offset fin. In other words, in the inner fin 3, the first fin portion 31 has the smallest air flowing resistance. In the present embodiment, the second fin portion 32 has the higher heat exchange performance, but the larger air flowing resistance, as compared to that of the third fin portion 33. That is, the first fin portion 31 is configured to have an air flowing resistance, the third fin portion 33 is configured to have an air flowing resistance larger than that of the first fin portion 31, and the second fin portion 32 is configured to have an air flowing resistance larger than that of the third fin portion 33.

Even this arrangement of the second embodiment, the entire heat exchanging performance can be effectively improved similarly to the above-mentioned first embodiment.

Third Embodiment

A third embodiment of the present invention will be described below based on FIG. 7. The same components as those in the first embodiment are designated by the same reference numerals, and a description thereof will be omitted below. FIG. 7 is a sectional view showing an inner fin 3 of the third embodiment when being viewed in the stacking direction of tubes 2. FIG. 7 is a diagram corresponding to the diagram of FIG. 3.

As shown in FIG. 7, the inner fin 3 of the present embodiment includes two first fin portions 31 each of which is a straight fin similar to that of the first embodiment, and a second fin portion 32 which is a louver fin similar to that of the first embodiment. The two first fin portions 31 are disposed one by one on the upstream and downstream sides of the second fin portion 32 in the flow direction of intake air. In other words, the second fin portion 31is disposed between the two first fin portions 31 in the flow direction of the intake air.

The two first fin portions 31 may be set to have substantially the same length in the flow direction of the intake air. The second fin portion 32 has substantially a symmetric shape with respect to a center line L1 in the intake-air flowing direction. Thus, the inner fin 3 of the present embodiment has substantially a symmetric shape with respect to a center line L2 of the entire inner fin 3 in the intake-air flowing direction. That is, the first and second fin portions 31 and 32 are disposed so as to be symmetrical to each other with respect to the center line L2 of the inner fin 3 in the intake-air flowing direction. At this time, the center line L1 of the second fin portion 32 in the intake-air flowing direction is substantially the same as the center line L2 of the inner fin 3 in the intake-air flowing direction.

The intercooler with this arrangement can prevent the wrong assembly of the inner fin 3 to the tube 2, while obtaining the same effects as those of the first embodiment.

Other Embodiments

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.

For example, in each of the above-mentioned embodiments, the different kinds of fin portions 31 to 33 are employed as fin portions with different specifications, the present invention is not limited thereto. The fin portions with different specifications may be constructed by setting the same kind of fins to have different respective fin pitches. In this case, a fin portion with the largest fin pitch among the fin portions is disposed on the upstream side of the intake-air flowing direction with respect to at least the other fin portions, thereby reducing the loss in pressure on the intake air inlet side of the tube 2. As a result, the entire intercooler can have an improved heat exchange performance.

Fin portions with different specifications may be constructed by employing the louver fin as the inner fin 3 and by setting the louver fins to have different louver pitches. In this case, a fin portion with the largest louver pitch among the fin portions is disposed on the upstream side of the intake-air flowing direction with respect to at least the other fin portions, so as to reduce the loss in pressure on the intake air inlet side of the tube 2. As a result, the entire intercooler can have improved heat exchange performance.

Although in the first and third embodiments the louver fin is used as the second fin 32, the present invention is not limited thereto. Alternatively, an offset fin may be used as the second fin 32.

In the second embodiment, the first fin portion 31, the third fin portion 33, and the second fin portion 32 are arranged in that order from the upstream side of the intake air flow. However, the first fin portion 31, the second fin portion 32, and the third fin portion 33 may be arranged in that order from the upstream side of the intake air flow.

Furthermore, the above embodiments of the present invention may be suitably combined without being limited to the above-described example.

For example, according an aspect of the above described embodiments and modifications of the present invention, a heat exchanger includes a tube 2 having therein a flow passage through which a first fluid flows, and an inner fin 3 provided in the tube 2. The tube 2 is adapted to exchange heat between the first fluid and a second fluid flowing through an outer periphery of the tube 2, and the inner fin 3 is located in the tube 2 to promote the heat exchange between the first fluid and the second fluid. The inner fin 3 is configured to divide the flow passage in the tube 2 into a plurality of flow paths 20. Furthermore, the inner fin 3 includes a plurality of fin portions (31, 32, 33) with different specifications, and the fin portions (31, 32, 33) are arranged in series with respect to a flow direction of the first fluid. In addition, the fin portion (31) with the smallest flowing resistance of the first fluid among the plurality of fin portions (31, 32, 33) is arranged on an upstream side of the flow direction of the first fluid with respect to at least an another fin portion (32, 33). Accordingly, the heat exchange performance in the heat exchanger can be effectively increased.

The phrase “the fin portion (31) with the smallest flowing resistance of the first fluid is arranged on the upstream side of the flow direction of the first flow with respect to at least an another fin portion (32, 33)” as used herein means not only that the fin portion (31) with the smallest flowing resistance of the first fluid is arranged only on the upstream side of the first fluid flow with respect to the other fin portions (32, 33), but also the following case. That is, the phrase also means that the fin portion (31) with the smallest flowing resistance of the first fluid is arranged on the upstream side of the first fluid flow, and the fin portion (31) with the smallest flowing resistance of the first fluid may be also arranged on the downstream side of the first fluid flow with respect to the other fin portions (32, 33). When the fin portion (31) with the smallest flowing resistance of the first fluid is arranged on the upstream side of the flow direction of the first fluid with respect to at least an another fin portion (32, 33) with a flowing resistance of the first fluid larger than the smallest flowing resistance, the specification such as the shape of the other fin portion(s) (32, 33) can be suitably changed.

For example, the fin portion (31) with the largest flowing resistance of the first fluid among the plurality of fin portions (31, 32, 33) may be arranged on a downstream side of the flow direction of the first fluid with respect to the other fin portion (32, 33).

Alternatively, the fin portions (31, 32, 33) may be arranged symmetrically with respect to a center line L2 of the inner fin in the flow direction of the first fluid. Furthermore, the fin portions (31, 32, 33) may be constructed of at least first and second different kinds of fin portions. For example, the plurality of fin portions (31, 32, 33) may include a straight fin portion 31 and a louver fin portion 32, and the straight fin portion 31 is arranged on an upstream side of the flow direction of the first fluid with respect to the louver fin portion 32. In this case, the straight fin portion 31 may have a plurality of wall surfaces 30 extending linearly in the flow direction of the first fluid, and the wall surfaces 30 may be configured to divide the flow passage of the tube into the plurality of flow paths. Furthermore, the louver fin portion may include a plurality of flat portions 3 a substantially in parallel to the flow direction of the first fluid, and a plurality of louvers 321 may be provided at the flat portions 3 a along the flow direction of the first fluid. As an example, the louvers 321 may be formed by cutting and raising a part of the flat portion.

Alternatively, the plurality of fin portions (31, 32, 33) may include a straight fin portion 31 and an offset fin portion 33, and the straight fin portion 31 may be arranged on an upstream side of the flow direction of the first fluid with respect to the offset fin portion 33. In this case, the straight fin portion 31 has a plurality of wall surfaces 30 extending linearly in the flow direction of the first fluid, and the wall surfaces 30 are configured to divide the flow passage of the tube 2 into the plurality of flow paths. Furthermore, the offset fin portion 33 including wall portions 333 are arranged in a zigzag shape along the flow direction of the first fluid, and the wall portions 333 are configured to divide the flow passage of the tube 2 into the plurality of flow paths.

Alternatively, the inner fin may be a single louver fin including a plurality of flat portions 3 a substantially in parallel to the flow direction of the first fluid, and a plurality of louvers 321 provided at the flat portions 3 a along the flow direction of the first fluid. In this case, the fin portions are configured to have different louver pitches in the louvers 321, and the fin portion with the largest louver pitch among the plurality of fin portions 321 is arranged on an upstream side of the flow direction of the first fluid with respect to at least an another fin portion.

Alternatively, in the heat exchanger, the fin portions may have different fin pitches. In this case, the fin portion with the largest fin pitch among the fin portions is arranged on an upstream side of the flow direction of the first fluid, with respect to at least an another fin portion.

In any above-described structure of the heat exchanger, the fin portions (31, 32, 33) may be continuously arranged in the flow direction of the first fluid such that flow resistances of the first fluid in the fin portions (31, 32, 33) are increased as toward downstream in the flow direction of the first fluid. Furthermore, in the heat exchanger, the first fluid flowing in the tube 2 generally may have a temperature higher than that of the second fluid. For example, the first fluid is an intake air to be supplied to an internal combustion engine, and the second fluid is a cooling air (i.e., outside air).

Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims. 

1. A heat exchanger comprising: a tube having therein a flow passage through which a first fluid flows, the tube being adapted to exchange heat between the first fluid and a second fluid flowing through an outer periphery of the tube; and an inner fin provided in the tube to promote the heat exchange between the first fluid and the second fluid, the inner fin being configured to divide the flow passage in the tube into a plurality of flow paths, wherein the inner fin includes a plurality of fin portions with different specifications, the fin portions are arranged in series with respect to a flow direction of the first fluid, and the fin portion with the smallest flowing resistance of the first fluid among the plurality of fin portions is arranged on an upstream side of the flow direction of the first fluid with respect to at least an another fin portion.
 2. The heat exchanger according to claim 1, wherein the fin portion with the largest flowing resistance of the first fluid among the plurality of fin portions is arranged on a downstream side of the flow direction of the first fluid with respect to the other fin portion.
 3. The heat exchanger according to claim 1, wherein the fin portions are arranged symmetrically with respect to a center line of the inner fin in the flow direction of the first fluid.
 4. The heat exchanger according to claim 1, wherein the fin portions are constructed of at least first and second different kinds of fin portions.
 5. The heat exchanger according to claim 1, wherein the plurality of fin portions include a straight fin portion having a plurality of wall surfaces extending linearly in the flow direction of the first fluid, the wall surfaces being configured to divide the flow passage of the tube into the plurality of flow paths, and a louver fin portion including a plurality of flat portions substantially in parallel to the flow direction of the first fluid, and a plurality of louvers provided at the flat portions along the flow direction of the first fluid, the louvers being formed by cutting and raising a part of the flat portion, wherein the straight fin portion is arranged on an upstream side of the flow direction of the first fluid, with respect to the louver fin portion.
 6. The heat exchanger according to claim 1, wherein the plurality of fin portions include a straight fin portion having a plurality of wall surfaces extending linearly in the flow direction of the first fluid, the wall surfaces being configured to divide the flow passage of the tube into the plurality of flow paths, and an offset fin portion including wall portions arranged in a zigzag shape along the flow direction of the first fluid, the wall portions being configured to divide the flow passage of the tube into the plurality of flow paths, wherein the straight fin portion is arranged on an upstream side of the flow direction of the first fluid, with respect to the offset fin portion.
 7. The heat exchanger according to claim 1, wherein the inner fin is a louver fin including a plurality of flat portions substantially in parallel to the flow direction of the first fluid, and a plurality of louvers provided at the flat portions along the flow direction of the first fluid, the louver being formed by cutting and raising a part of the flat portion, the fin portions are configured to have different louver pitches in the louvers, and the fin portion with the largest louver pitch among the plurality of fin portions is arranged on an upstream side of the flow direction of the first fluid, with respect to at least an another fin portion.
 8. The heat exchanger according to claim 1, wherein the fin portions have different fin pitches, and the fin portion with the largest fin pitch among the fin portions is arranged on an upstream side of the flow direction of the first fluid, with respect to at least an another fin portion.
 9. The heat exchanger according to claim 1, wherein the fin portions are continuously arranged in the flow direction of the first fluid such that flow resistances of the first fluid in the fin portions are increased as toward downstream in the flow direction of the first fluid.
 10. The heat exchanger according to claim 1, wherein the first fluid flowing in the tube generally has a temperature higher than that of the second fluid.
 11. The heat exchanger according to claim 1, further comprising: a plurality of the tubes each of which defines therein the refrigerant passage in which the first fluid flows, the tubes being stacked in a stacking direction; and a plurality of outer fins each of which is located between adjacent tubes. 